1. Field of the Invention
The present invention relates to an optical switch for use in optical fiber communication and optical network technology, and particularly to an optical switch having four reflecting surfaces.
2. Description of Related Art
Optical signals are commonly transmitted in optical fibers, which provide efficient light channels through which the optical signals can pass. Recently, optical fibers have been used in various fields, including telecommunications, where light passing through an optical fiber is used to convey either digital or analog information. Efficient switching of optical signals between individual fibers is necessary in most optical processing systems or networks to achieve the desired routing of the signals.
A typical switch has one or more light input port(s) and at least two light output ports for performing switching or logical operations to optical signals in a light transmitting line/system or in an integrated optical circuit. Factors for assessing the capability of an optical switch include low insertion loss (IL,  less than 1 db), good isolation performance ( greater than 50 db), and fast switching speed (normally, tens of milliseconds).
Optical switches are divided into two types. One is mechanical type and the other is non-mechanical type. In principle, the mechanical type optical switches have a number of advantages over other forms of optical switches in such applications where switching speed is not critical. Mechanical type optical switches offer lower insertion losses, low cross-talk, and insensitivity to wavelength of light.
Conventional mechanical type optical switches come in two different designs: where the optical components move, and where the fibers move. Moving fiber switches involve the actual physical movement of one or more of the fibers to specific positions to accomplish the transmission of a beam of light from one fiber end to another fiber end under selected switching conditions. Moving optical component switches, on the other hand, include optical collimating lenses which expand the beam of light from the fibers, and then, using moving prisms or mirrors, reswitch the expanded beam as required by the switching process.
The moving fiber switches have a stringent tolerance requirement for the amount and direction of fiber movement. The tolerance is typically a small portion of the fiber core diameter for two fibers to precisely collimate to reduce loss. The fibers themselves are quite thin and may be subject to breakage if not properly protected. On the other hand, reinforcing the fibers with stiff protective sheaths makes fiber into alignment. Thus these moving fiber optical switches share a common problem of requiring high precision parts to obtain precise positioning control and low insertion loss. This results in high costs and complicates manufacture of the switches. Moreover, frequently moving fibers to and fro is apt to damage or even break the fibers. The switching speed of these moving fiber optical switches is also slow.
Conventional moving optical component switches have less stringent movement control tolerance requirements because of the collimating lenses.
A moving optical component switch, as disclosed in U.S. Pat. No. 5,436,986 and shown in FIG. 6, comprises a first and a second input fibers 101, 103, a first and a second output fibers 102, 104, and a driving device 304 and a movable reflector assembly 200. The movable reflector assembly 200 includes a movable block 203 and two reflectors 201, 202 assembled on the block 203. Each reflector has two reflecting surfaces for reflecting light beams from the input fibers 101, 103. The driving device 304 drives the movable reflector assembly 200 to move between a first position and a second position. When the movable reflector assembly 200 is displaced in the first position, light beams from the first and second input fibers 101, 103 are directly transmitted to the first and second output fibers 104, 102. When the movable reflector assembly 200 is displaced in the second position, the reflector 201 reflects off the light beams from the first input fiber 101 to the reflector 202, and the reflector 202 reflects off the light beams to the second output fiber 102; the reflector 202 reflects off the light beams from the second input fiber 103 to the reflector 201, and then the reflector 201 reflects off the light beams to the first output fiber 104.
In this mechanical optical switch, the light beams are reflected two times, which increases the insertion loss. Furthermore, each reflector has two reflecting surfaces fixed thereon for reflecting light beams from different input fibers, and four reflecting surfaces of the movable reflector assembly 200 are at the path of the light beams at the same time, so it is very difficult to adjust the positions of the fibers and the reflecting surfaces for precisely collimating light beams from the input fibers 101, 103 to the corresponding output fibers 102, 104.
For the above reasons, an improved optical switch which has high optical efficiency, is easy to align and does not require movement of the optical fibers themselves is desired.
An object of the present invention is to provide an optical switch which is easy to adjust and has a low insertion loss.
Another object of the present invention is to provide an optical switch which uses four reflecting surfaces as a switching element.
In accordance with one aspect of the present invention, an optical switch comprises two input ports, two output ports and a movable reflector assembly. The movable reflector assembly includes a first reflector and a second reflector and moves between a first position and a second position. The first reflector includes two reflecting surfaces, and the second reflector also includes two reflecting surfaces. The first input port is opposite to the second output port, and the second input port is parallel to the first output port. When the movable reflector assembly is in the first position, the first reflector is in the path of the light beams while the second reflector is out of the path of the light beams, the light beams from the first input port are reflected by one reflecting surface of the first reflector and enter the first output port, and the light beams from the second input port are reflected by the other reflecting surface of the first reflector and enter the second output port. When the movable reflector assembly is in the second position, the first reflector is out of the path of the light beams while the second reflector blocks the path of the light beams, the light beams from the first input port directly travel toward the second output port, and the light beams from the second input port are reflected twice by the two reflecting surfaces of the second reflector and enter the first output port.
The feature of the present invention is to move the first and second reflectors into the path of the light beams in turn and reduce the insertion loss and the difficulty of adjustment.
Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.